Top Description Fields Constructors Methods
org.apache.poi.util

public Class RLEDecompressingInputStream

extends InputStream
Class Inheritance
Imports
java.io.IOException, .InputStream, java.util.Locale, org.apache.commons.io.input.UnsynchronizedByteArrayInputStream, org.apache.commons.io.output.UnsynchronizedByteArrayOutputStream
Wrapper of InputStream which provides Run Length Encoding (RLE) decompression on the fly. Uses MS-OVBA decompression algorithm. See http://download.microsoft.com/download/2/4/8/24862317-78F0-4C4B-B355-C7B2C1D997DB/[MS-OVBA].pdf

Field Summary

Modifier and TypeField and Description
private final byte[]
buf

a byte buffer with size 4096 for storing a single chunk

private final InputStream
in

the wrapped inputstream

private int
len

the number of bytes in the byte buffer

private int
pos

the current position in the byte buffer for reading

private static final int[]
POWER2

Bitmasks for performance

Constructor Summary

AccessConstructor and Description
public
RLEDecompressingInputStream(InputStream
The stream to wrap with the RLE Decompression
in)

Creates a new wrapper RLE Decompression InputStream.

Method Summary

Modifier and TypeMethod and Description
public int
available()

Overrides java.io.InputStream.available.

Returns an estimate of the number of bytes that can be read (or skipped over) from this input stream without blocking, which may be 0, or 0 when end of stream is detected.

public void
close()

Overrides java.io.InputStream.close.

Implements java.io.Closeable.close.

Closes this input stream and releases any system resources associated with the stream.

public static byte[]
decompress(byte[] compressed)

public static byte[]
decompress(byte[] compressed, int offset, int length)

pack-priv static int

Returns:

returns the number of bits in the copy token (a value between 4 and 12)
getCopyLenBits(int offset)

Helper method to determine how many bits in the CopyToken are used for the CopyLength.

public int
read()

Implements abstract java.io.InputStream.read.

Reads the next byte of data from the input stream.

public int
read(byte[]
the buffer into which the data is read.
b)

Overrides java.io.InputStream.read.

Reads some number of bytes from the input stream and stores them into the buffer array b.

public int
read(byte[]
the buffer into which the data is read.
b, int
the start offset in array b at which the data is written.
off, int
the maximum number of bytes to read.
l)

Overrides java.io.InputStream.read.

Reads up to len bytes of data from the input stream into an array of bytes.

private int

Returns:

number of bytes that were read, or -1 if the end of the stream was reached.
readChunk()

Reads a single chunk from the underlying inputstream.

public int

Returns:

integer value from the stream, -1 if end of stream is reached
readInt()

Convenience method for read a 4-bytes int in little endian encoding.

private int
readInt(InputStream stream)

public int

Returns:

short value from the stream, -1 if end of stream is reached
readShort()

Convenience method for read a 2-bytes short in little endian encoding.

private int
readShort(InputStream stream)

public long
skip(long
the number of bytes to be skipped.
n)

Overrides java.io.InputStream.skip.

Skips over and discards n bytes of data from this input stream.

Inherited from java.io.InputStream:
markmarkSupportednullInputStreamreadAllBytesreadNBytesreadNBytesresetskipNBytestransferTo

Field Detail

bufback to summary
private final byte[] buf

a byte buffer with size 4096 for storing a single chunk

inback to summary
private final InputStream in

the wrapped inputstream

lenback to summary
private int len

the number of bytes in the byte buffer

posback to summary
private int pos

the current position in the byte buffer for reading

POWER2back to summary
private static final int[] POWER2

Bitmasks for performance

Constructor Detail

RLEDecompressingInputStreamback to summary
public RLEDecompressingInputStream(InputStream in) throws IOException

Creates a new wrapper RLE Decompression InputStream.

Parameters
in:InputStream

The stream to wrap with the RLE Decompression

Method Detail

availableback to summary
public int available()

Overrides java.io.InputStream.available.

Doc from java.io.InputStream.available.

Returns an estimate of the number of bytes that can be read (or skipped over) from this input stream without blocking, which may be 0, or 0 when end of stream is detected. The read might be on the same thread or another thread. A single read or skip of this many bytes will not block, but may read or skip fewer bytes.

Note that while some implementations of InputStream will return the total number of bytes in the stream, many will not. It is never correct to use the return value of this method to allocate a buffer intended to hold all data in this stream.

A subclass's implementation of this method may choose to throw an IOException if this input stream has been closed by invoking the close() method.

Returns:int

an estimate of the number of bytes that can be read (or skipped over) from this input stream without blocking or 0 when it reaches the end of the input stream.

Annotations
@Override
closeback to summary
public void close() throws IOException

Overrides java.io.InputStream.close.

Implements java.io.Closeable.close.

Doc from java.io.InputStream.close.

Closes this input stream and releases any system resources associated with the stream.

Annotations
@Override
Exceptions
IOException:
if an I/O error occurs.
decompressback to summary
public static byte[] decompress(byte[] compressed) throws IOException
decompressback to summary
public static byte[] decompress(byte[] compressed, int offset, int length) throws IOException
getCopyLenBitsback to summary
pack-priv static int getCopyLenBits(int offset)

Helper method to determine how many bits in the CopyToken are used for the CopyLength.

Returns:int

returns the number of bits in the copy token (a value between 4 and 12)

readback to summary
public int read() throws IOException

Implements abstract java.io.InputStream.read.

Doc from java.io.InputStream.read.

Reads the next byte of data from the input stream. The value byte is returned as an int in the range 0 to 255. If no byte is available because the end of the stream has been reached, the value -1 is returned. This method blocks until input data is available, the end of the stream is detected, or an exception is thrown.

Returns:int

the next byte of data, or -1 if the end of the stream is reached.

Annotations
@Override
Exceptions
IOException:
if an I/O error occurs.
readback to summary
public int read(byte[] b) throws IOException

Overrides java.io.InputStream.read.

Doc from java.io.InputStream.read.

Reads some number of bytes from the input stream and stores them into the buffer array b. The number of bytes actually read is returned as an integer. This method blocks until input data is available, end of file is detected, or an exception is thrown.

If the length of b is zero, then no bytes are read and 0 is returned; otherwise, there is an attempt to read at least one byte. If no byte is available because the stream is at the end of the file, the value -1 is returned; otherwise, at least one byte is read and stored into b.

The first byte read is stored into element b[0], the next one into b[1], and so on. The number of bytes read is, at most, equal to the length of b. Let k be the number of bytes actually read; these bytes will be stored in elements b[0] through b[k-1], leaving elements b[k] through b[b.length-1] unaffected.

Parameters
b:byte[]

the buffer into which the data is read.

Returns:int

the total number of bytes read into the buffer, or -1 if there is no more data because the end of the stream has been reached.

Annotations
@Override
Exceptions
IOException:
If the first byte cannot be read for any reason other than the end of the file, if the input stream has been closed, or if some other I/O error occurs.
readback to summary
public int read(byte[] b, int off, int l) throws IOException

Overrides java.io.InputStream.read.

Doc from java.io.InputStream.read.

Reads up to len bytes of data from the input stream into an array of bytes. An attempt is made to read as many as len bytes, but a smaller number may be read. The number of bytes actually read is returned as an integer.

This method blocks until input data is available, end of file is detected, or an exception is thrown.

If len is zero, then no bytes are read and 0 is returned; otherwise, there is an attempt to read at least one byte. If no byte is available because the stream is at end of file, the value -1 is returned; otherwise, at least one byte is read and stored into b.

The first byte read is stored into element b[off], the next one into b[off+1], and so on. The number of bytes read is, at most, equal to len. Let k be the number of bytes actually read; these bytes will be stored in elements b[off] through b[off+k-1], leaving elements b[off+k] through b[off+len-1] unaffected.

In every case, elements b[0] through b[off-1] and elements b[off+len] through b[b.length-1] are unaffected.

Parameters
b:byte[]

the buffer into which the data is read.

off:int

the start offset in array b at which the data is written.

l:int

the maximum number of bytes to read.

Returns:int

the total number of bytes read into the buffer, or -1 if there is no more data because the end of the stream has been reached.

Annotations
@Override
Exceptions
IOException:
If the first byte cannot be read for any reason other than end of file, or if the input stream has been closed, or if some other I/O error occurs.
readChunkback to summary
private int readChunk() throws IOException

Reads a single chunk from the underlying inputstream.

Returns:int

number of bytes that were read, or -1 if the end of the stream was reached.

readIntback to summary
public int readInt() throws IOException

Convenience method for read a 4-bytes int in little endian encoding.

Returns:int

integer value from the stream, -1 if end of stream is reached

readIntback to summary
private int readInt(InputStream stream) throws IOException
readShortback to summary
public int readShort() throws IOException

Convenience method for read a 2-bytes short in little endian encoding.

Returns:int

short value from the stream, -1 if end of stream is reached

readShortback to summary
private int readShort(InputStream stream) throws IOException
skipback to summary
public long skip(long n) throws IOException

Overrides java.io.InputStream.skip.

Doc from java.io.InputStream.skip.

Skips over and discards n bytes of data from this input stream. The skip method may, for a variety of reasons, end up skipping over some smaller number of bytes, possibly 0. This may result from any of a number of conditions; reaching end of file before n bytes have been skipped is only one possibility. The actual number of bytes skipped is returned. If n is negative, the skip method for class InputStream always returns 0, and no bytes are skipped. Subclasses may handle the negative value differently.

Parameters
n:long

the number of bytes to be skipped.

Returns:long

the actual number of bytes skipped which might be zero.

Annotations
@Override
Exceptions
IOException:
if an I/O error occurs.